Ink composition for inkjet spacer formation and spacer element using the same

ABSTRACT

The present invention relates to an ink composition for spacer formation and a spacer element using the same, and more particularly to an ink composition for spacer formation including a) 10 to 70 parts by weight (dry weight) of a polymer emulsion; b) 0.1 to 50 parts by weight of weight of wetting agent; and c) 20 to 90 parts by weight of solvent, and a spacer element using the same. The ink composition of the present invention has a significantly low viscosity and can be sprayed easily by inkjet, so that it is useful for spacer formation in liquid crystal displays.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an ink composition for spacer formationused for color televisions, computer monitors, and other displaydevices, and a spacer element using the same.

(b) Description of the Related Art

Demand for color liquid crystal displays has been on the increase inrecent years, and large liquid crystal displays are being manufactured.However, manufacturing costs should be reduced in order for the colordisplay devices to be used more widely.

Conventionally, a liquid crystal display is manufactured by forming aliquid crystal driving device, such as a TFT (thin film transistor), anda coloring device, such as a color filter, on a pair of opposingtransparent insulating substrates. Between the substrates there arespacers that maintains a 3 to 10 μm space therebetween. Liquid crystalis injected in this space, and then the spacing is sealed to form aliquid crystal device.

Conventionally, spherical or cylindrical silica, alumina, or syntheticresin particles randomly distributed between the TFT substrate and thecolor filter substrate have been used as the spacer. But, in this case,the spacer around the light passage of the liquid crystal display mayhinder driving of the liquid crystal or deteriorate the display qualitydue to the optical properties of the spacer itself.

In order to solve this problem, a method of selectively forming a spacerin the black matrix formation part through which no light passes, usinga photoresist substance, has been proposed. In this case, the blackmatrix blocks the display quality-deteriorated part, and thusdeterioration of display quality can be avoided.

However, when using a photoresist, the spacer formation process requiresmany steps including spin coating, pre-baking, exposure, developing, andpost-baking of the spacer substance, and therefore the manufacturingcost increases.

To solve this problem, Korea Patent Publication No. 2001-0049941, JapanPatent Publication No. 2001-109002, and Japan Patent Publication No.2001-83525 proposed a method for selectively forming a spacer on theblack matrix through which no light passes, by the inkjet process.

Korea Patent Publication No. 2001-0049941 and Japan Patent PublicationNo. 2001-83525 proposed a cross-linking spacer-forming substance, whichcould be sprayed by the inkjet head, and which used a homopolymer orcopolymer as a cross-linkable substance. Usage of the substance waslimited from 0.01 to 30 parts by weight. During spacer formation, thesprayed solvent is evaporated in the cross-linking step, and only thehomopolymer or copolymer forms the spacer. While the diameter of the inkdroplet on the substrate surface remains almost the same due to itsadhesivity, its height decreases, so that the height of the final spacerbecomes significantly lower than that of the ink droplet. Accordingly,the height becomes insufficient for a high-resolution black matrix,which requires a small diameter.

In addition, Japan Patent Publication No. 2001-109002 proposed that itis preferable to use a monomer or oligomer with a low molecular weight,considering the spraying characteristics of the ink, while limiting thecontent of the solvent under 50 parts by weight and increasing thecontent of the spacer-forming substance. However, a substance with a lowmolecular weight does not have sufficient mechanical properties unlessit is fully cross-linked, and light exposure or heat treatment forsufficient cross-linking increases manufacturing time and decreasesproductivity.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an inkjet ink(hereunder, ink) composition having a significantly low viscosity andthat is easily inkjet-sprayable by adding a cross-linking agent in anemulsion, which is obtained by dispersing a polymer with a relativelyhigh molecular weight with an emulsifier, so that cross-linking by lightexposure or heat treatment can be done in a short time.

Another object of the present invention is to provide a spacer formed byusing the ink composition.

Still another object of the present invention is to provide a liquidcrystal display comprising the spacer.

To attain these objects, the present invention provides an inkcomposition for spacer formation, comprising:

-   -   a) 10 to 70 parts by weight (dry weight) of a polymer emulsion;    -   b) 0.1 to 50 parts by weight of a wetting agent; and    -   c) 20 to 90 parts by weight of a solvent.

The present invention also provides a spacer formed by the inkcomposition.

In addition, the present invention provides a liquid crystal displaycomprising the spacer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the spacer formation process of thepresent invention.

FIG. 2 is a schematic diagram of the liquid crystal display comprisingthe spacer of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention is described in more detail.

The present invention relates to an ink composition for preciselyforming a spacer on one of the two opposing substrates of a liquidcrystal display, by the inkjet method.

Polymer chains of the polymer emulsion used in the present invention aresurrounded by an emulsifying agent, not by water, and therefore thepolymer emulsion has an almost spherical microstructure. Therefore,there is little entanglement between the polymer chains, differentlyfrom the system wherein the polymer chains are disentangled lengthily ina solvent.

Accordingly, an ink composition using the polymer emulsion has a muchlower viscosity than a polymer solution having a comparableconcentration and molecular weight, and therefore spraying by inkjet ismuch easier. Also, because even a hardly-soluble polymer can beemulsified using an appropriate emulsifying agent, a variety of polymersmay be used to prepare ink. Also, because a polymer with a largemolecular weight can be used without significantly increasing theviscosity of the ink, it is possible to prepare ink having goodprocessability and capacity.

The ink composition of the present invention comprises a) a polymeremulsion, b) a wetting agent, and c) a solvent.

a) The polymer emulsion of the present invention is the basic materialfor forming the spacer. It has sufficient hardness and elasticity,superior heat resistance and chemical resistance, and sufficientadhesivity to the substrate surface. Also, it has a sufficiently lowviscosity, preferably a viscosity of 3 to 50 cp, so that it can besprayed by inkjet when prepared as ink.

Preferably, the polymer emulsion is selected from a group consisting ofan acryl emulsion, a urethane acryl emulsion, an epoxy acryl emulsion, apolyester acryl emulsion, and any mixture thereof. However, it is notlimited to said polymer emulsions. Preferably, the polymer emulsion hasa molecular weight of 300 to 50,000.

Preferably, the polymer emulsion is used at from 10 to 70 parts byweight (dry weight). If the dry solid content of the polymer emulsion isbelow 10 parts by weight, the final height of the spacer becomes low.Otherwise, if it exceeds 70 parts by weight, it is difficult to obtain astable emulsion.

b) The wetting agent of the present invention may be selected from agroup consisting of: glycols, such as ethylene glycol, propylene glycol,diethylene glycol, triethylene glycol, and polyethylene glycol;glycerine; ethers of polyhydric alcohols, such as diethylene glycolmonobutyl ether; acetates; thioglycol; and amino acids, such as glycine,methyl glycine, lucine, proline, alanine, and phenyl alanine.

Preferably, b) the wetting agent is used from 0.1 to 50 parts by weight.If the content of the wetting agent is below 0.1 part by weight, the inkmay become dry around the nozzle, and thus it may not spray. Otherwise,if it exceeds 50 parts by weight, the solid content of the inkdecreases, and therefore the final height of the spacer may become low.

Preferably, c) the solvent is selected from a group consisting of water,acetone, methyl ethyl ketone, methyl isobutyl ketone, methylcellosolve,ethylcellosolve, tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethylether, ethylene glycol diethyl ether, propylene glycol methyl ether,propylene glycol dimethyl ether, propylene glycol diethyl ether,chloroform, methylene chloride, 1,2-dichloroethane,1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,2-trichloroethene,hexane, heptane, octane, cyclohexane, benzene, toluene, xylene,methanol, ethanol, isopropanol, propanol, butanol, t-butanol,cyclohexanone, propylene glycol methyl ether acetate, propylene glycolethyl ether acetate, 3-methoxybutyl acetate, ethyl 3-ethoxy propionate,ethylcellosolve acetate, methylcellosolve acetate, butyl acetate, methylethyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether,y-butyl lactone, N-methylpyrrolidone, dimethylformamide,tetramethylsulfone, ethylene glycol acetate, ethyl ether acetate, ethyllactate, polyethylene glycol, and cyclohexanone.

Preferably, the solvent is used from 20 to 90 parts by weight. If thecontent of the solvent is below 20 parts by weight, the viscosity of theink increases, so that it is not sprayed well. Otherwise, if it exceeds90 parts by weight, the solid content of the ink decreases, andtherefore the final height of the spacer may become low.

The ink composition of the present invention may further comprise d) across-linking initiator and a cross-linking promoter, e) a polymericcompound having unsaturated bonds, or f) other additives to control theinkjet spraying characteristics and the physical properties and form ofthe spacer. In the case the ideal properties can be obtained with onlya) the polymer emulsion, d) the cross-linking initiator and thecross-linking promoter, and e) the polymeric compound having unsaturatedbonds, may not be added. That is, if the polymer emulsion has a largemolecular weight, the spacer has good physical properties, so that it isnot necessary to add a cross-linking initiator and a cross-linkingpromoter, or a polymeric compound having unsaturated bonds. But,spraying from the inkjet nozzle may be somewhat difficult.

d) The cross-linking initiator and the cross-linking promoter of thepresent invention are water-soluble or soluble to the emulsifying agent.Initiation of cross-linking may be caused by light, heat, an electronbeam, and so forth.

Preferably, the cross-linking initiator is selected from a groupconsisting of: biimidazole compounds, such as2,2′-bis(2-chlorophenyl)-4,4′,5,5′-tetraphenyl biimidazole and2,2′-bis(2,3-dichlorophenyl)-4,4′,5,5′-tetraphenylbiimidazole;acetophenone compounds, such as2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propane,2-hydroxy-2-methyl-1-phenylpropan-1-one,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,4-(2-hydroxyethoxy)-phenyl(2-hydroxy)propyl ketone, 1-hydroxycyclohexylphenyl ketone, benzoin methyl ether, benzoin ethyl ether, benzoinisobutyl ether, benzoin butyl ether, 2,2-dimethoxy-2-phenylacetophenone, 2-methyl-(4-methylthiophenyl)-2-morpholino-1-propan-1-one,and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one;benzophenone compounds, such as benzophenone,4,4′-bis(dimethylamino)benzophenone, 4,4′-bis(diethylamino)benzophenone,2,4,6-trimethylaminobenzophenone, methyl-o-benzoyl benzoate,3,3-dimethyl-4-methoxybenzophenone, and3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophenone; fluorenonecompounds, such as 9-fluorenone, 2-chloro-9-fluorenone, and2-methyl-9-fluorenone; thioxantone compounds, such as thioxantone,2,4-diethyl thioxantone, 2-chloro thioxantone, 1-chloro-4-propyloxythioxantone, isopropyl thioxantone, and diisopropyl thioxantone;xanthone compounds, such as xanthone and 2-methylxanthone; anthraquinonecompounds, such as anthraquinone, 2-methyl anthraquinone, 2-ethylanthraquinone, t-butyl anthraquinone, and2,6-dichloro-9,10-anthraquinone; acridine compounds, such as9-phenylacridine, 1,7-bis(9-acridinyl)heptane,1,5-bis(9-acridinyl)pentane, and 1,3-bis(9-acridinyl)propane; dicarbonylcompounds, such asbenzyl-1,7,7-trimethyl-bischloro[2,2,1]heptane-2,3-dione and9,10-phenanthrenquinone; phosphine oxides, such as2,4,6-trimethylbenzoyl diphenylphosphine oxide,bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide, andbis(2,6-dichlorobenzoyl)propyl phosphine oxide; methyl4-(dimethylamino)benzoate; ethyl-4-(dimethylamino)benzoate; aminesynergists, such as 2-n-butoxyethyl 4-(dimethylamino)benzoate,2,5-bis(4-diethylaminobenzal)cyclopentanone,2,6-bis(4-diethylaminobenzal)cyclohexanone, and2,6-bis(4-diethylaminobenzal)-4-methyl-cyclohexanone; coumarincompounds, such as 3,3′-carbonylvinyl-7-(diethylamino)coumarin,3-(2-benzothiazolyl)-7-(diethylamino)coumarin,3-benzoyl-7-(diethylamino)coumarin, 3-benzoyl-7-methoxy-coumarin, and10,10′-carbonylbis[1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-Cl]-benzopyrano[6,7,8-ij]-quinolizin-11-one; calcon compounds, such as4-diethylamino calcon and 4-azidobenzalacetophenone; 2-benzoylmethylene;3-methyl-β-naphthothiazoline; and(4-methylphenyl)-[4-(2-methylpropyl)-phenyl]hexafluorophosphine iodide.And, preferably, the cross-linking promoter is selected from a groupconsisting of 2-mercaptobenzoimidazole, 2-mercaptobenzothiazole,2-mercaptobenzoxazole, 2,5-dimercapto-1,3,4-thiadizole,2-mercapto-4,6-dimethylaminopyridine, pentaerythritoltetrakis(3-mercaptopropionate), pentaerythritoltris(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate),pentaerythritol tris(2-mercaptoacetate), trimethylolpropanetris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate),trimethylolethane tris(2-mercaptoacetate), and trimethylolethanetris(3-mercaptopropionate).

Preferably, the cross-linking initiator and the cross-linking promoterare used at less than 10 parts by weight.

Preferably, e) the ethylene polymeric compound having unsaturated bondsof the present invention is selected from a group consisting of:compounds obtained by esterification of polyhydric alcohols withα,β-unsaturated carboxylic acids, such as ethylene glycoldi(meth)acrylate, (poly)ethylene glycol di(meth)acrylate having 2 to 14ethylene groups, trimethylolpropane di(meth)acrylate, trimethylolpropanetri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, propylene glycol di(meth)acrylate having 2 to 14propylene groups, dipentaerythritol penta(meth)acrylate, anddipentaerythritol hexa(meth)acrylate; compounds obtained by adding(meth)acrylic acid to glycidyl-containing compounds, such as atrimethylolpropane triglycidyl ether acrylic acid adduct and a bisphenolA diglycidyl ether acrylic acid adduct; esters of compounds havinghydroxy groups or ethylene unsaturated bonds and polycarboxylic acids oradducts with polyisocyanates, such as a phthalic acid diester ofβ-hydroxyethyl(meth)acrylate and a toluene diisocyanate adduct ofβ-hydroxyethyl(meth)acrylate; and (meth)acrylic acid alkyl esters, suchas methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate, and2-ethylhexyl(meth)acrylate.

Preferably, the polymeric compound having unsaturated bonds is used atless than 40 parts by weight.

Preferably, f) the other additives are selected from a group consistingof: silicon-based antifoaming agents; surface tension controlling agentsfor cationic, anionic, zwitterionic, and non-ionic surfactants; UVabsorbers, such as benzotriazole or benzophenone; light stabilizers,such as phenols or amines; anti-biocontaminants such aschloromethylphenols; chelating agents such as EDTA; oxygen absorbentssuch as sulfites; and thermal polymerization inhibitors, such asp-anisole, hydroquinone, pyrocatechol, t-butylcatechol, andphenothiazine. Preferably, the additives are used at less than 5 partsby weight.

In the present invention, any compounds that are comprised inconventional inkjet ink compositions may be used for the additives of d)to f) for said purposes.

The ink composition of the present invention is sprayed onto adetermined position of the substrate from an inkjet head. The sprayedink forms a droplet on the substrate. Then, the substrate is heated orleft alone at room temperature to evaporate the solvent from the ink.The spacer is formed by and cross-linking reaction using light, heat,electron beams, etc., if required.

Accordingly, the present invention can precisely form a spacer at anideal position on at least one of the two opposing substrates of aliquid crystal display by the inkjet method.

FIG. 1 is a schematic diagram of the spacer formation process of thepresent invention, and FIG. 2 is a schematic diagram of the liquidcrystal display comprising the spacer of the present invention. In saiddrawings, the vertical dotted lines show that the spacer formed by theinkjet is positioned at a black matrix formation part of a color filtersubstrate.

Hereinafter, the present invention is described in more detail throughExamples and a Comparative Example. However, the following Examples areonly for the understanding of the present invention, and the presentinvention is not limited by the following Examples.

EXAMPLE 1

63 parts by weight of Neocryl (Zeneca); 20 parts by weight of glycerol,15 parts by weight of water, and 2 parts by weight of CX100 (Zeneca) asa cross-linking emulsion were mixed well to prepare an acryl emulsion,and then filtered with a 2.5-μm filter. The viscosity was 11 cp. Theemulsion was sprayed through an inkjet nozzle on a glass substrate onwhich a transparent electrode or an alignment film was formed. Then, thesubstrate was dried at 80° C. for 2 minutes to evaporate the solvent,and thermal cross-linking was carried out at 150° C. for 30 minutes. Asa result, a spacer with of a diameter of 25 μm and a height of 4 μm wasformed. The hardness of the spacer was over 4H.

EXAMPLE 2

70 parts by weight of Ebecryl (UCB), 15 parts by weight of glycerol, and15 parts by weight of water were mixed to prepare an acryl emulsion, andthen filtered with a 2.5-μm filter. The viscosity was 15 cp. A spacerwas formed as in Example 1, while omitting the thermal cross-linkingstep. As a result, a spacer with a diameter of 27 μm and a height of 4.5μm was formed. The hardness of the spacer was over 2H.

COMPARATIVE EXAMPLE

47 parts by weight of polyethylene glycol diacrylate, a water-solublemonomer, 20 parts by weight of ethoxytrimethylolpropane triacrylateester, 10 parts by weight of glycerol, 20 parts by weight of water, and3 parts by weight of Irgacure 2959 (Ciba Specialty Chemicals) as a photoinitiator were mixed to prepare ink by the conventional method, and thenfiltered with a 2.5-μm filter. The viscosity was 27 cp. The ink wassprayed through an inkjet nozzle on a glass substrate. After 3 minutesof pre-baking at 70° C., UV was irradiated for 3 minutes and post-bakingwas carried out at 150° C. for 30 minutes. As a result, a spacer with adiameter of 50 μm and a height of 3 μm and a satellite of a meter of 10μm and a height of 1 μm were formed. The hardness of the spacer wasabout HB.

Because the ink comprising the polymer emulsions of Examples 1 and 2 hada much lower viscosity than the polymer solution of Comparative Example,spraying by inkjet was easy. Additionally, the spacer formed with theink comprising the polymer emulsion with a large molecular weight hadbetter mechanical hardness than the spacer formed by the ink comprisingthe polymer solution. Also, as in Example 2, some spacers showed goodhardness without a cross-linking step.

As described above, the ink composition for spacer formation of thepresent invention has a significantly low viscosity and can be easilysprayed by inkjet, so that it is useful for spacer formation in liquidcrystal displays.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A composition for spacer formation in a liquid crystal display,having a viscosity of 3 to 50 cp and comprising: a) 10 to 70 parts byweight (dry weight) of a polymer emulsion; b) 0.1 to 50 parts by weightof wetting agent; and c) 20 to 90 parts by weight of a solvent, whereinthe polymer emulsion has a molecular weight of 300 to 50,000, whereinthe polymer emulsion is selected from the group consisting of an acrylemulsion, a urethane acryl emulsion, an epoxy acryl emulsion, apolyester acryl emulsion, and any mixture thereof, and wherein thewetting agent is selected from the group consisting of glycols,glycerine, ethers of polyhydric alcohols, acetates of polyhydricalcohols, thioglycol, and amino acids.
 2. The composition according toclaim 1, wherein c) the solvent is selected from a group consisting ofwater, acetone, methyl ethyl ketone, methyl isobutyl ketone,methylcellosolve, ethylcellosolve, tetrahydrofuran, 1,4-dioxane,ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propyleneglycol methyl ether, propylene glycol dimethyl ether, propylene glycoldiethyl ether, chloroform, methylene chloride, 1,2-dichloroethane,1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,2-trichloroethene,hexane, heptane, octane, cyclohexane, benzene, toluene, xylene,methanol, ethanol, isopropanol, propanol, butanol, t-butanol,cyclohexanone, propylene glycol methyl ether acetate, propylene glycolethyl ether acetate, 3-methoxybutyl acetate, ethyl 3-ethoxy propionate,ethylcellosolve acetate, methylcellosolve acetate, butyl acetate, methylethyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether,γ-butyrolactone, N-methylpyrrolidone, dimethylformamide,tetramethylsulfone, ethylene glycol acetate, ethyl ether acetate, ethyllactate, polyethylene glycol, and cyclohexanone.
 3. The compositionaccording to claim 1, which further comprises d) less than 10 parts byweight of a cross-linking initiator and a cross-linking promoter; or e)less than 40 parts by weight of polymeric compound having unsaturatedbonds.
 4. The composition according to claim 1, which further comprisesf) less than 5 parts by weight of additives selected from a groupconsisting of an antifoarning agent, a surface tension controllingagent, a light stabilizer, an anti-biocontaminant, an oxygen absorbent,and a thermal polymerization inbibitor.
 5. A spacer formed by thecomposition according to claim
 1. 6. A liquid crystal display comprisingthe spacer according to claim 5.